This invention relates to a lid lifting mechanism and more particularly for assisting in lifting heavy lids of various types of vessels such as pressure vessels.
Counter balancing systems for lid lifting mechanisms are well known. Examples of such systems are described in U.S. Pat. Nos. 3,555,732, 3,561,162 and 4,145,843. These various types of lid lifting mechanisms involved counter balancing springs which are interposed between the container and the lid by a mechanical linkage such that when an attempt is made to open the lid, the energy stored in the lid lifting mechanism is released to assist in raising the lid.
A device for assisting in lifting heavier lids such as manhole covers is described in U.S. Pat. No. 5,038,520. A pretensioned spring is connected to a lever arm which is in turn connected to the lid. Upon raising the manhole cover the pretensioned spring inserts pressure on the lever arm to rotate the lid about its pivot point and assist in raising the lid. The pretensioned spring can be set to provide the correct amount of compressive energy to exert the proper amount of force in assisting in opening the lid.
U.S. Pat. Nos. 3,144,165 and 3,310,329 describe lid opening systems for pressure vessels. Both systems rely on motive power from a pressure cylinder or electric motor so that there is more than enough power to raise the lid. In U.S. Pat. No. 3,144,165, an electric motor rotates a screw which is connected to a threaded device at the end of a lever arm attached to the lid by actuating the motor the screw retracts the threaded device along its length thereby raising the lid to the open position. Sufficient power may be designed into the motor to open the lid as the lever arm pivots about its pivot point. Similarly in U.S. Pat. No. 3,310,329, a fluid driven piston is provided which when retracted moves the lid to the open position by pulling down on an arm member attached to the lid. These systems are quite substantial in structure and require periodic maintenance due to the nature of the power drives.
It is an object of an aspect of this invention to provide a lid lifting mechanism which is mechanically actuated so that it is inexpensive to build and easy to maintain.
It is an object of an aspect of this invention to provide a lid lifting mechanism for assisting in pivoting to an open position, a lid for a vessel, the mechanism comprises:
i) a pivot arm adapted to be secured to a vessel lid, the pivot arm having a pivot mount intermediate its length, the pivot arm extending beyond the pivot mount to provide a distal end;
ii) a pretensioned retracting device for assisting in pivoting the arm from a lid closed to a lid open position, and means for adjusting retracting device tension;
iii) a connector for connecting the retracting device to the distal end, means for mounting the connector on the arm distal end for movement along the arm to increase or decrease moment arm length of the retracting device relative to the pivot mount and thereby adjust extent of retracting device assist in pivoting the lid to a lid open position.